The present invention relates to a brake apparatus for a vehicle, and more particularly to the apparatus capable of applying a regulator pressure regulated by a regulator valve device to an assisting chamber formed backward of a master piston.
In general, as for the brake apparatus capable of applying the regulator pressure to the assisting chamber formed backward of the master piston, it is disclosed in Japanese Patent No. 3101205, for example. That is, the brake apparatus includes a master piston, which is fluid-tightly slidably disposed in a cylinder body, to form a pressure chamber in front of the master piston and a power chamber behind it, and moved in response to operation of a manually operated braking member, to discharge a hydraulic braking pressure from the pressure chamber, an auxiliary hydraulic pressure source which pressurizes the brake fluid up to a predetermined pressure, and discharges a power pressure, a control piston which is fluid-tightly slidably accommodated in the cylinder body and arranged to be moved in response to movement of the control piston, and regulator valve means which introduces the power pressure discharged from the auxiliary hydraulic pressure source into a regulator chamber, to regulate the power pressure into a predetermined pressure in response to movement of the control piston. The hydraulic pressure regulated by the regulator valve means is applied to the power chamber of the master cylinder, to assist the operation of the manually operated braking member. With respect to the brake apparatus capable of applying the regulator pressure regulated by the regulator valve means to the power chamber (assisting chamber) as described above, Japanese Patent Laid-open Publication No. 11-180290 discloses hydraulic pressure relationships among various parts, in detail.
Recent vehicles require an automatic braking control, which is adapted to measure a distance or speed difference between a vehicle by a driver and another vehicle traveling ahead thereof to determine a necessity for decreasing the vehicle speed, and perform a braking operation automatically to decrease the vehicle speed, unless a vehicle driver operates an accelerator pedal, and which is called as “ACC” (abbreviation of “Adaptive Cruise Control”). And, a control apparatus which is capable of performing the automatic braking control is getting popular. During the automatic braking control operation as described above, when a vehicle driver operates a brake pedal, the automatic braking operation shall be cancelled, and shifted to the braking operation performed in response to operation of the brake pedal by the vehicle driver.
For example, Japanese Patent Laid-open Publication No. 2000-108859 proposes a braking control apparatus, which is aimed to perform the automatic braking operation, and cancel it, when it is detected that the brake pedal has been operated by a driver, and discloses an embodiment using a hydraulic booster as an actuator. According to this braking control apparatus, the vehicle can be braked automatically, so as to keep a certain distance between the vehicle driven by the driver and another vehicle traveling ahead thereof detected by a sensor, and can be braked to provide an emergent braking operation.
Also, Japanese Patent No. 3296235 proposes a braking force control apparatus, which is aimed to produce a hydraulic braking pressure larger than a normal pressure, when the emergent braking operation was performed by the vehicle driver, and reflect an intention of the vehicle driver on the hydraulic braking pressure, and which is capable of performing a so-called brake assist control. For example, there are provided an increased assisting pressure state for holing the hydraulic braking pressure larger than the normal pressure, and a decreased assisting pressure state for decreasing the hydraulic braking pressure irrespective of operation of the brake pedal.
As described in the Japanese Patent Laid-open Publication No. 2000-108859 or Japanese Patent No. 3296235, as for the automatic braking control apparatus for performing an automatic pressure increasing control as required, irrespective of operation of the brake pedal, to perform the braking operation automatically, various types of the apparatus have been known heretofore, so that their controlling state are different depending upon their objects, and their responses, which are taken when the automatic braking operation is shifted to the brake pedal operation by the vehicle driver, are different from each other. Particularly, in the case where the brake pedal is operated by the driver, in such a state that the braking operation is being performed, as a result of determination that the distance between the vehicle driven by the driver and another vehicle traveling ahead thereof has become to be smaller than a predetermined distance, for example, such as the above-described automatic braking control, it is desired that a smooth brake feeling shall be given to the driver.
However, according to the braking control apparatuses as disclosed in the Japanese Patent Laid-open Publication No. 2000-108859 or Japanese Patent No. 3296235, when the braking operation is shifted to the one operated by the brake pedal, there may be a case where the smooth brake feeling can not be expected. As described in paragraphs [0054] and [0055] of the Publication No. 2000-108859, for example, when the hydraulic pressure is fed from an accumulator to all of front and rear wheels, the brake pedal will hardly stroke, to provide a so-called “depressing board” state, which is inappropriate. Also, the Publication No. 2000-108859 discloses an embodiment, where the brake pressure shall not be supplied to a front wheel brake cylinder not to be controlled, during the automatic braking operation. According to this embodiment, the brake pressure will be supplied only to rear wheel brake cylinders, during the automatic braking operation, so that a desired braking operation may not be performed.
Furthermore, the braking control performed by the apparatus as described in Japanese Patent No. 3296235 is different from the braking control according to the present invention, which is performed by the braking control apparatuses as described in Japanese Patent No. 3101205 and Publication No. 11-180290, so that the relationships of the pressures in the braking control apparatuses are different from each other. Therefore, countermeasures as described in Japanese Patent No. 3296235 can not be employed, as they are. Particularly, while the brake assist operation is being performed in case of the emergent braking operation, the communication between the master cylinder and wheel brake cylinder is forced to be blocked, so that the “depressing board” feeling will be given to the driver. In order to avoid this, such a countermeasure as providing a so-called stroke simulator will be required.